I too have learned something in this discussion. A couple of observations:

You should measure the AC input current required to produce that 80 amps of DC charging. Due to efficiency losses and poor power factor, it is much more than your 10% efficiency loss calculation would indicate. I remember the spec on our 2.5 KW and 100 amp Freedom charger. It said it drew 21 amps AC (at 120V) to produce 100 amps of DC at 12 V. I actually measured about 17 amps AC. Still that is about 70% more than theoretical current.

I used the hot water heater (calorifier if you will) to keep the genset loaded. After about an hour of charging as the current dropped off, I would turn on the heater breaker and it would absorb another 1.5 KW for about 30 minutes until the thermostat tripped off. Then I would shut down the generator. Batteries were about 85% charged at that point.

One thing you can do with a DC charger to keep it loaded that hasn't been mentioned is to reduce the rpm. If you reduce a 1,500 rpmengine (keeping the numbers consistent with your side of the Atlantic) to 1,000 rpm then you will keep the load up and with a good controller, your DC output won't drop significantly. Use of your inverter to dump excess KW into the calorifier will also help as with the AC genset.

Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)

Boat: Cutter-Rigged Moody 54

Posts: 19,743

Re: Charge Cycle Generator

Quote:

Originally Posted by djmarchand

Dockhead:

I too have learned something in this discussion. A couple of observations:

You should measure the AC input current required to produce that 80 amps of DC charging. Due to efficiency losses and poor power factor, it is much more than your 10% efficiency loss calculation would indicate. I remember the spec on our 2.5 KW and 100 amp Freedom charger. It said it drew 21 amps AC (at 120V) to produce 100 amps of DC at 12 V. I actually measured about 17 amps AC. Still that is about 70% more than theoretical current.

I used the hot water heater (calorifier if you will) to keep the genset loaded. After about an hour of charging as the current dropped off, I would turn on the heater breaker and it would absorb another 1.5 KW for about 30 minutes until the thermostat tripped off. Then I would shut down the generator. Batteries were about 85% charged at that point.

One thing you can do with a DC charger to keep it loaded that hasn't been mentioned is to reduce the rpm. If you reduce a 1,500 rpm engine (keeping the numbers consistent with your side of the Atlantic) to 1,000 rpm then you will keep the load up and with a good controller, your DC output won't drop significantly. Use of your inverter to dump excess KW into the calorifier will also help as with the AC genset.

David

Like use, I use the calorifier and also oil-filled radiators to keep my genset loaded. It's basically free heat since below 25% load or so, the fuelconsumption of the genset does not fall below 1 liter per hour.

BUT such a tactic shows the fundamental inefficiency of lightly loaded gensets. I think that the thing to learn from this is that chasing some incremental gain in theoretical efficiency is a big waste of time -- since we're all dumping power into heat from time to time anyway. I don't think that effciency of the conversion from liters of diesel to final power is the most important or even third most important design value. Besides dumping power into heat, don't forget, we are not spending a majority of genset hours driving the charger in bulk charging mode, either. We would kill our batteries if we did that. We all spend a lot of time just letting the genset run so that the batteries can creep up to a higher state of charge, which they need for their health. And so the biggest inefficiency in the system of all is what happens inside the lead-acid batteries. This inefficiency dwarfs any other possible inefficiency in the system, making them basically irrelevant.

My Victron charger takes about 10 amps of AC power at 230 volts when it is running at full tilt, pumping 80 amps into my batteries. So at least at the highest charging rates, the loss does seem to be about 10%. Caveat: measured with analogue ammeter orignal to the boat, so might not be all that accurate.

As to reducing RPM of a DC charger -- fine, but again, that's a very small incremental increase in efficiency. Running a bit slower, versus carrying the same load at a higher constant RPM. I think it matters very little when that constant RPM is 1500.

... First most small AC gens put out a peak sign wave somewhere below 150 loaded, and I have seen em all the way down to 140 ...

How does that work?

Since the RMS (root-mean-square) voltage of a pure symmetrical sine wave is approximately
0.707 x peak voltage; hence at 120V RMS, the peak will be (120 ÷ 0.707) ≈ 170V.
This relationship should hold true for any RMS voltage.

At a peak voltage of 150V, I'd expect the metered RMS voltage to be only about 106V.

__________________
Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

Boat: Sold Sigma 33 OOD some time ago, will be chartering in Turkey really soon

Posts: 358

Re: Charge Cycle Generator

Quote:

Originally Posted by GordMay

How does that work?

Since the RMS (root-mean-square) voltage of a pure symmetrical sine wave is approximately
0.707 x peak voltage; hence at 120V RMS, the peak will be (120 ÷ 0.707) ≈ 170V.
This relationship should hold true for any RMS voltage.

At a peak voltage of 150V, I'd expect the metered RMS voltage to be only about 106V.

Like Gord I do not really understand the effective AC voltage issue. I'm sure AC generators are quoted using effective voltage which is the average (RMS) of the sine wave. I do understand the RPM bit; never thought of that one; with DC you do need need to worry about cycles and can simply lower RPM; it would still leave the engine partly unloaded; diesels like 80% load, that is where they are most efficient and run the best (longest).

Assuming just your charger running at full out that's 1680 watts, that puts you at just below 25% load, at 1.1 LPH

In my case I'm putting out 3770 watts at 1 LPH, so assuming the battery is down to 50% SOC I can recharge to 80% in half the time, half the fuel as your setup.

Now all of this really depends on the size of the bat bank, as well as the health of the bats. A small bank is going to be less efficient, and recharging will be most efficient during bulk for both systems.

My bank is 720 amp hr, so I can draw it down 360 amp hrs(50% SOC) it takes 3 days on my average loads. But I need domestic HW for shower and dishes. So I run my gen for an 1.5 hrs every other day. With my Isotemp HW heater on this cycle I have the needed domestic HW. The dc gen makes the HW as a byproduct of charging the bats. We shower, and do dishes, and vacuuming during the run cycle. Then we have enough HW to last until the next run cycle, so we can shower daily, and do dishes morning and night.

This can also be done with a prime AC gen, but very few are set up this way, and just use the ac element of the HW.

And yes my unit will run at 1000 rpm during absorption cycle, and the fuel consumption will drop by 2/3, but it will still make all the domestic HW I can use. The problem associated with light loading aren't as bad, bc the alternator is still loading the engine for this amp out to rpm ratio. Also prior to shut down I can speed it back up for 1-2 minutes and resolve any carbon build up.

Now about the regulator. The Balmar controller that I use, is completely programmable, exceeding anything possible that the Victron Charger is. I can map the ramps to and from BULK, Absorption, and Float, I can map the charge voltages for each cycle, I can map the duration in each cycle. All of this mapping is independent for each cycle. The controller is both bat. and alternator temp. compensated....so I can never over heat the bat, nor the alternator, these temp. comps. are also completely adjustable.

I don't have anything against Victron, I rather like there products, and have installed many Victron units, including chargers and Inv/Charg. I have never put a scope on your gen, but I have scopped the NorthernLights gen of the same size, and can tell you that Ive seen the peakV drop to 160.

So really my point is everything depends on how it's set up, and the type of use the system is designed for. One does not fit all, but amps into the bank my money is on DC CCG.

One thing for everyone to consider is to actually check your system, bc I know there are many systems that are under performing.

This will probably drive a couple of large Inverters should you find that you can't live with out the ubiquitous air conditioner.

Once again thanks to you and all the other posters for contributing to this informative discussion. I am learning a lot and am always grateful for any knowledge being imparted.

I have looked at those units, here in the Seattle area a number were sold, and most have been problamatic. I know of at least 6 units removed. They are a very complicated piece of equipment. I don't like there charge control, it is all based on engine speed. They have a history of running hot when they have a big bulk cycle. They are high costs at purchase and for maintenance. Must be serviced by someone who has gone to F..P.. College.

My system is very simple, on-boards spares can be carried, and easily replaced by someone with basic mechanical skills.

The 3.4 kw unit is a single cylinder Kabota, which has poor thermodynamics especially when in a sound shield, vibrates under heavy load.

I have just had a look at the owners manual for the AGT6000. Wow now that's a lot of dc power. But I certainly would want to see and talk with an owner of this unit before I made any decisions, after it has some run time. What is the price?, and for sure other then oil changes this unit will require someone schooled by F..P..

"At a peak voltage of 150V, I'd expect the metered RMS voltage to be only about 106V"

What the OP was saying, and I never appreciated this", is that while suppliing power to a charger (with poor power factor control and other bad electrical characteristics), the generator's output sine wave is clipped, making it look more like a square wave. True rms voltage of a square wave equals the peak voltage.

My point about reducing rpm wasn't necessarily to improve efficiency which as someone pointed out was marginal. It was to increase the load on the engine to improve longevity. Lightly loaded genset engines are subject to cylinder glazing, which dramatically increases oil consumption, and reduces compression and performance.

There is a boat electrical supply system that solves almost all of these problems. It is made by Mastervolt and is called their Hybrid generator. It is a multipole, high frequency generator that effectively is rectified and drives an integral inverter to produce AC power. The whole thing is in one package and all you have to do is hook it up to some external batteries. The genset puts out about 3kw, the inverter 2kw, and the two are additive for 5 kw continuously and I suspect 6-7 kw momentarily to start inductive loads. The genset starts and stops automatically depending on battery voltage.

But I am sure that it isn't cheap. You could make your own with a small generator and a Victon inverter/charger with genset start capability.

Assuming just your charger running at full out that's 1680 watts, that puts you at just below 25% load, at 1.1 LPH

In my case I'm putting out 3770 watts at 1 LPH, so assuming the battery is down to 50% SOC I can recharge to 80% in half the time, half the fuel as your setup.

Now all of this really depends on the size of the bat bank, as well as the health of the bats. A small bank is going to be less efficient, and recharging will be most efficient during bulk for both systems.

My bank is 720 amp hr, so I can draw it down 360 amp hrs(50% SOC) it takes 3 days on my average loads. But I need domestic HW for shower and dishes. So I run my gen for an 1.5 hrs every other day. With my Isotemp HW heater on this cycle I have the needed domestic HW. The dc gen makes the HW as a byproduct of charging the bats. We shower, and do dishes, and vacuuming during the run cycle. Then we have enough HW to last until the next run cycle, so we can shower daily, and do dishes morning and night.

This can also be done with a prime AC gen, but very few are set up this way, and just use the ac element of the HW.

And yes my unit will run at 1000 rpm during absorption cycle, and the fuel consumption will drop by 2/3, but it will still make all the domestic HW I can use. The problem associated with light loading aren't as bad, bc the alternator is still loading the engine for this amp out to rpm ratio. Also prior to shut down I can speed it back up for 1-2 minutes and resolve any carbon build up.

Now about the regulator. The Balmar controller that I use, is completely programmable, exceeding anything possible that the Victron Charger is. I can map the ramps to and from BULK, Absorption, and Float, I can map the charge voltages for each cycle, I can map the duration in each cycle. All of this mapping is independent for each cycle. The controller is both bat. and alternator temp. compensated....so I can never over heat the bat, nor the alternator, these temp. comps. are also completely adjustable.

I don't have anything against Victron, I rather like there products, and have installed many Victron units, including chargers and Inv/Charg. I have never put a scope on your gen, but I have scopped the NorthernLights gen of the same size, and can tell you that Ive seen the peakV drop to 160.

So really my point is everything depends on how it's set up, and the type of use the system is designed for. One does not fit all, but amps into the bank my money is on DC CCG.

One thing for everyone to consider is to actually check your system, bc I know there are many systems that are under performing.

Lloyd

By all means, do convince me -- I like having weak points in my own prejudices destroyed.

The big new thing I learned from this post is the capabilities of the Balmar regulator. I was totally unaware that they, or any other alternator regular, could be programmed to that extent. It sounds exactly like what I can do (and have done) with my Victron, which is programmable by laptop over its built-in Ethernet port. It sounds like I need to have one of those. I have an Adverc regulating a 110 amps * 24v Leece-Neville alternator. It works fine, but it takes forever to get the batteries up. It works on a principle which might be good for the long-term health of the batteries -- will give them 30 minute shots of high voltage, with 30 minutes of rest in between. But as a way to get charge into the batteries quickly it leaves a lot to be desired.

You did not say what size your battery bank is. Mine is 440ah * 24 volts. The 80 amps my Victron produces is about as much as I'm comfortable with putting into them in bulk mode. Maybe you have a bigger battery bank.

Your setup sounds great, and it sounds like a great achievement to have designed it yourself. Doing something like that yourself is either a big plus or a big minus depending on time and enthusiasm. I am not convinced that it is a great deal better than a coventional solution, but still my hat is off to you.

I do like very much the idea that you can throttle it down while batteries are in absorption mode and keep taking heat out of it. You probably will be using a bit less fuel than I do, but as I said, I don't think that a fraction of a liter per hour in the grand scheme of things is going to be an important value for anyone (other than the subjective satisfaction of achieving it -- the elegance of efficiency!). You have inspired me to speed up my work on splicing a heat exchanger into my genset cooling system.

My Kohler manual says that the genset produces about 8kW of heat at full load. I suppose I met get half of that maybe - ? - out of an efficient heat exchanger. That is not nearly enough to heat my boat (I have a 10kW Eberspaecher for that), but it is definitely a useful amount of heat which is a shame to dump into the ocean.

Three cylinders running at 1500 RPM will be more durable, much quieter, and produce much less vibration than two cylinders at 2400 -- there is a big dfference between two and three cylinders. But your setup will be quieter when throttled down, which is good. And as you point out, your setup is quite a bit lighter than mine. If you assign some value to your time, of which I have no doubt you spent enormous amounts on this project, then your setup will have been much more expensive than mine, dwarfing any small savings in fuel. But I'm sure you did it for the satisfaction of producing something like that yourself, not to save money.

Your view of my fuel economy is somewhat optimistic -- 80 amps of charging loads my genset to 10 amps or about 40%, so I'm using closer to 1.5 liters per hour when the charger is putting out its full output in bulk mode (over 2000 watts). But over the long run, 0.5 liters per hour, over some hundreds of hours of run time for a few years of cruising, is chump change, compared to the capital expense of the system. Anyway we all add other other loads, even unreasonable ones (from efficiency standpoint) like water and space heating, so fuel is just not being managed to within fractions of liters per hour, however you slice it.

Concerning the electronic performance of AC gensets, you have given me new information. I never heard that these problems are so serious. I know that my own system does not underproduce charge rates due to waveform problems, and looking at the oscilloscope screenshots from the Victron test, it does not look to me like better-quality heavy-duty AC gensets have waveform problems even at high loads. But you have given me something to think about, and to discuss with people who understand electrickery better than I do. It's an interesting question. If I find out more, I will post here, and maybe I'll put a scope on my own genset sometime if I have the opportunity.

I agree with you about the Fischer-Panda gensets. The theory behind them is good (much like your setup). But the implentation is terrible, in my opinion, using overstressed, complex systems for applications which should be, on the contrary, simple and understressed, and therefore reliable and foolproof. I especially dislike the ones with one cylinder engines screaming away at 3600 RPM in sealed boxes. And practical use shows that they are not very satisfactory. Your system is vastly better, in my opinion. Good luck with it!

Diesels produce more heat than HP at the shaft, average 40% HP, the rest in heat, the remaining heat generated is about 40% exhaust, 40% cooling/radiator, the balance goes out radiation.

With a typical sea water cooled Mani-cooler, we can recover 1/3 to 1/2 of this heat.

So in my case that gives me 6860 potential watts heat from that same liter of fuel. That's about 23,420 BTU hrs of heat for the boat. During summer months I only capture the heat for domestic HW about 7-9,000 BTU, but during colder months when heating the boat is needed, I can capture close to all of it.

But really I measure efficiency..by how little time my gen runs 1.5 hrs out of 48 is over 97% efficient.

By all means, do convince me -- I like having weak points in my own prejudices destroyed.

The big new thing I learned from this post is the capabilities of the Balmar regulator. I was totally unaware that they, or any other alternator regular, could be programmed to that extent. It sounds exactly like what I can do (and have done) with my Victron, which is programmable by laptop over its built-in Ethernet port. It sounds like I need to have one of those. I have an Adverc regulating a 110 amps * 24v Leece-Neville alternator. It works fine, but it takes forever to get the batteries up. It works on a principle which might be good for the long-term health of the batteries -- will give them 30 minute shots of high voltage, with 30 minutes of rest in between. But as a way to get charge into the batteries quickly it leaves a lot to be desired.

I have have installed dozens of these over the years...In 12 years I have never seen one fail.

Quote:

You did not say what size your battery bank is. Mine is 440ah * 24 volts. The 80 amps my Victron produces is about as much as I'm comfortable with putting into them in bulk mode. Maybe you have a bigger battery bank.

Your setup sounds great, and it sounds like a great achievement to have designed it yourself. Doing something like that yourself is either a big plus or a big minus depending on time and enthusiasm. I am not convinced that it is a great deal better than a coventional solution, but still my hat is off to you.

I do like very much the idea that you can throttle it down while batteries are in absorption mode and keep taking heat out of it. You probably will be using a bit less fuel than I do, but as I said, I don't think that a fraction of a liter per hour in the grand scheme of things is going to be an important value for anyone (other than the subjective satisfaction of achieving it -- the elegance of efficiency!). You have inspired me to speed up my work on splicing a heat exchanger into my genset cooling system.

My Kohler manual says that the genset produces about 8kW of heat at full load. I suppose I met get half of that maybe - ? - out of an efficient heat exchanger. That is not nearly enough to heat my boat (I have a 10kW Eberspaecher for that), but it is definitely a useful amount of heat which is a shame to dump into the ocean.

Three cylinders running at 1500 RPM will be more durable, much quieter, and produce much less vibration than two cylinders at 2400 -- there is a big dfference between two and three cylinders. But your setup will be quieter when throttled down, which is good. And as you point out, your setup is quite a bit lighter than mine. If you assign some value to your time, of which I have no doubt you spent enormous amounts on this project, then your setup will have been much more expensive than mine, dwarfing any small savings in fuel. But I'm sure you did it for the satisfaction of producing something like that yourself, not to save money.

Your view of my fuel economy is somewhat optimistic -- 80 amps of charging loads my genset to 10 amps or about 40%, so I'm using closer to 1.5 liters per hour when the charger is putting out its full output in bulk mode (over 2000 watts). But over the long run, 0.5 liters per hour, over some hundreds of hours of run time for a few years of cruising, is chump change, compared to the capital expense of the system. Anyway we all add other other loads, even unreasonable ones (from efficiency standpoint) like water and space heating, so fuel is just not being managed to within fractions of liters per hour, however you slice it.

I pulled the numbers for your gen from the Kholer manual, but those may or may not represent actual.

Based on Perkins rating of my engine life running 2800 rpm, in excess of 6k hrs, I don't think with my duty cycle I'll have much to worry about.

Quote:

Concerning the electronic performance of AC gensets, you have given me new information. I never heard that these problems are so serious. I know that my own system does not underproduce charge rates due to waveform problems, and looking at the oscilloscope screenshots from the Victron test, it does not look to me like better-quality heavy-duty AC gensets have waveform problems even at high loads. But you have given me something to think about, and to discuss with people who understand electrickery better than I do. It's an interesting question. If I find out more, I will post here, and maybe I'll put a scope on my own genset sometime if I have the opportunity.

No matter the manufactures claims I always choose real world numbers, and sometimes that requires testing.

Quote:

I agree with you about the Fischer-Panda gensets. The theory behind them is good (much like your setup). But the implentation is terrible, in my opinion, using overstressed, complex systems for applications which should be, on the contrary, simple and understressed, and therefore reliable and foolproof. I especially dislike the ones with one cylinder engines screaming away at 3600 RPM in sealed boxes. And practical use shows that they are not very satisfactory. Your system is vastly better, in my opinion. Good luck with it!

I am only basing it from my experience, and I certainly don't want to slam anyone's products...As I said my info is old and maybe there has been improvement...that I'm not aware, problems can be sorted out with growing manufacturing cycles.

Attached is a pic of a recent install of the Balmar controllers. I was relegated to using 90 amp alts on this twin engine because there was no other way to add dbl pulleys. So that meant I needed to add the centerfielder to the regs to charge the single house bank, then I added a digital duo-charge to maintaint the start bank.

Interesting! Don't want to re-engineer the wheel although some things I do wonder about when comparing an alternator against a well designed inverter/charger.

One that come to mind is the copper wiring resistance that has a positive temperature coefficient that means the hotter the wire gets, the higher its resistance becomes.

Balmar reduces their high current alternators as a the alternator temperatures increase.......so for example, a 200 ampere alternator is 200 ampere only when the alternator temperatures are not high. Just increasing the circular mils of the wire may not be the answer. Larger diameter (circular mils) is compromised by skin effect which forces current to flow nearer the outer surfaces of the wire. Skin effect is caused by the magnetizing field at a distance from the center of the wire.

Then there is the temperature in the bilge that governs how well the alternator can be cooled.

AHHhhh..... the entropy of it all! But when converting energy to engine HP one needs to be careful. For example, a 10 or for that matter a 100HP engine develops that rated output usually a high RPM. That is why many of today's generators are 2 pole instead of 4 poles and they scream to 3600RPM vs 1800RPM. So if one really needs 5HP at low RPM, he may require a 10HP engine to get it.